Earth is the third planet from the sun. It takes 365.25 days to revolve around the sun. It rotates about its tilted axis, 23.4 degrees from the perpendicular of its orbital plane. It is about 150,000,000km from the Sun or 1.0 (AU, Astronomical Unit). The earth's diameter is 12,756.3km and have a mass of 5.972e24kg. It's rotational velocity is about 1,674.4 km/h.

Surprisingly it is the densest planet in the solar system. It's density is 5.514 g/cm3. Inside the earth is divided into layers. These layers are inner core, outer core, D", lower mantle, transition region, upper mantle and crust.

The inner core is solid which is made up of iron and nickel. The outer core is also composed of iron and nickel but in liquid form. This core spins in the opposite direction of the Earth's rotation and this generates earth's magnetic field.

It's atmosphere is mostly nitrogen and about a fifth is oxygen. A layer of a form of oxygen, ozone high up in the atmosphere protects earth from perilous ultraviolet rays.

It has a natural satellite that is called moon. It is hypothesize that other growing planetary bodies hit the earth blowing out derbis. A fraction of these went into earth's orbit. This is how moon is believed to be formed.

It is the only known planet that supports life. (Credit:en.wikipedia.org/wiki/Earth)